Many products include components formed from nonwoven webs of polymeric fibers. Products such as filtration media, disposable surgical garments, disposable cleaning cloths, disposable personal cleansing wipes and towels, bandages and wound dressings, disposable diapers and training pants, adult incontinence pants and feminine hygiene pads are only a few examples.
Consumer products such as disposable diapers may include a number of components formed of nonwoven web materials, such as backsheet outer layers, topsheets, and barrier cuffs. The nonwoven web supply material is typically formed in a relatively wide, continuous sheet, which is then cut or slit to suitable cross direction widths and machine direction lengths to form components during the process of manufacturing such products. A typical disposable diaper may have a number of exposed cut edges of nonwoven web about its perimeter and/or other locations. Nonwoven web components other types of products may also have exposed cut edges.
The cut edges of such components are often formed in a relatively high speed process in which a nonwoven web is conveyed in the machine direction, through the nip of a cutting mechanism. The cutting mechanism may comprise a pair of offset circular blades with overlapping perimeter cutting edges that are formed and disposed to meet in shearing/scissors fashion, while rotating on axes above and below the web and approximately parallel with the cross direction, thereby continuously scissoring the web along the machine direction. In an alternative cutting mechanism, a rotating cutting blade having a perimeter cutting edge may be disposed to meet an opposing rotating anvil roller having a smooth surface, to form a cutting nip. Regardless which process may be used, there are shortcomings.
First, particularly when a cutting blade is less than fully sharp as after some use, as it encounters fibers in the web as the web is conveyed into the shearing/cutting nip, the dulled cutting edge may tend to displace the fibers within the web before severing them, in a manner similar to what occurs when one tries to cut a fibrous web with a dull scissors. As a result, the cut edge may have a ragged form and appearance rather than a neat, clean cut form and appearance. This can present complications in downstream processing. Further, if a product has nonwoven components with such ragged edges exposed, consumers may have negative perceptions of the quality of the product.
Second, in many types of nonwoven webs the individual fibers thereof may only be loosely bound within the web. Particularly in (but not unique to) webs formed of low bond area percentage or shorter fibers or staple fibers, cutting the web and further downstream operations may cause individual fibers that are randomly cut short near the edge in the shearing/cutting operation, and are not securely bound within the web, to work loose and be released into the plant environment. This may contribute to imparting to the cut edge an undesirable frayed structure and appearance, and, depending upon the severity of the situation, can create significant industrial hygiene problems. Loose fibers, often airborne, can accumulate and cause problems with plant environment equipment and processes. It is often necessary to install and operate costly vacuum systems to collect such fibers, and even these are not completely successful. Additionally, periodic shutdown of lines for removal of substantial accumulations of loose fibers is often necessary.
Regardless of whether the cutting blade used to cut the web is sharp and the web is formed of long fibers, fibers along cut edges may be displaced or dislodged in downstream operations, resulting in a frayed and/or uneven edge.
For these reasons, there is a need for improvement in the nonwoven web cutting, slitting and/or shearing process and the resulting product.